ntflag: New test

Signed-off-by: Andy Lutomirski <luto@kernel.org>

2 files changed, 55 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 6dfce9e..1447ecf 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ SIMPLE_C_TARGETS := dump-vsyscall context_switch_latency kernel_pf user_visible_
 
 SIMPLE_CC_TARGETS := evil-clock-test
 
-SPLIT_C_TARGETS := dump-vdso dump-vvar syscall_exit_regs dump_all_pmcs
+SPLIT_C_TARGETS := dump-vdso dump-vvar syscall_exit_regs dump_all_pmcs ntflag
 SPLIT_CC_TARGETS := timing_test test_vsyscall test_vdso_parser
 
 ALL_TARGETS := $(SIMPLE_C_TARGETS) $(SIMPLE_CC_TARGETS) $(SPLIT_C_TARGETS:%=%_64) $(SPLIT_CC_TARGETS:%=%_64) $(SPLIT_C_TARGETS:%=%_32) $(SPLIT_CC_TARGETS:%=%_32) syscall32_from_64 segregs
diff --git a/ntflag.c b/ntflag.c
new file mode 100644
index 0000000..b2233f4
--- /dev/null
+++ b/ntflag.c
@@ -0,0 +1,54 @@
+/*
+ * single_step_syscall.c - single-steps various x86 syscalls
+ * Copyright (c) 2014-2015 Andrew Lutomirski
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * Some obscure user-space code requires the ability to make system calls
+ * with FLAGS.NT set.  Make sure it works.
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <asm/processor-flags.h>
+
+#ifdef __x86_64__
+# define WIDTH "q"
+#else
+# define WIDTH "l"
+#endif
+
+static unsigned long get_eflags(void)
+{
+	unsigned long eflags;
+	asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
+	return eflags;
+}
+
+static void set_eflags(unsigned long eflags)
+{
+	asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
+		      : : "rm" (eflags) : "flags");
+}
+
+int main()
+{
+	printf("[RUN]\tSet NT and issue a syscall\n");
+	set_eflags(get_eflags() | X86_EFLAGS_NT);
+	syscall(SYS_getpid);
+	if (get_eflags() & X86_EFLAGS_NT) {
+		printf("[OK]\tThe syscall worked and NT is still set\n");
+		return 0;
+	} else {
+		printf("[FAIL]\tThe syscall worked but NT was cleared\n");
+		return 1;
+	}
+}